Divergent responses of soil microbial communities to water and nitrogen addition in a temperate desert

- Soil microbial communities were investigated under water and nitrogen (N) addition.
- Water addition increased microbial biomass, respiration, bacterial and fungal PLFAs.
- N addition had opposite effects on soil microbes in interplant and beneath shrubs.
- Water and N addition interactively affects soil microbes beneath shrubs.

Increasing precipitation and N deposition are reported in northern China. However, their impacts on soil microorganisms are still unclear. We aimed to elucidate how increasing precipitation and N deposition alone and in combination would affect soil microorganisms in interplant soils and beneath shrubs of Haloxylon ammodendron. A 30% increase in precipitation and 5 gN m− 2 yr− 1 addition were applied to simulate precipitation increasing and N deposition in a temperate desert steppe across 2011-2013. Increasing precipitation significantly increased microbial biomass carbon (MBC) and respiration (MR), as well as bacterial and fungal PLFAs. N addition slightly increased MBC, MR, as well as total, bacterial, and fungal PLFAs in interplant, while decreasing all of them beneath shrubs. N addition consistently increased microbial biomass nitrogen (MBN) at both microsites, but only decreased the ratio of MBC to MBN beneath shrubs. Both water and N addition had no impacts on the ratio of fungal to bacterial PLFAs (F:B), suggesting no impacts of water or N addition on microbial community composition. Microbial biomass, respiration, bacterial and fungal PLFAs were positively related to soil water content across treatments, suggesting that the increasing MR under increasing precipitation was mainly contributed by increasing microbial biomass rather than altering microbial community composition. In addition, the interaction of precipitation and N addition on microorganisms is discrepant between interplant and beneath shrubs, with significant effects beneath shrubs and no impacts in interplant. Our results support the hypothesis that water and N are co-limiting factors in desert ecosystems, but the effects are habitat-specific in deserts.